Ions have long been favored for many processes because their electric charge facilitates their manipulation by electrostatic and magnetic fields. This introduces great flexibility in processing. However, in some applications, the charge that is inherent to any ion (including gas cluster ions in a GCIB) may produce undesirable effects in the processed surfaces. GCIB has a distinct advantage over conventional ion beams in that a as cluster ion with a single or small multiple charges enables the transport and control of a much larger mass-flow (a cluster may consist of hundreds or thousands of molecules) compared to a conventional ion (a single ionized atom, molecule, or molecular fragment.) Particularly in the case of insulating materials, surfaces processed using ions often suffer from charge-induced damage resulting from abrupt discharge of accumulated charges, or production of damaging electrical field-induced stress in the material (again resulting from accumulated charges.) In many such cases, GCIBs have an advantage due to their relatively low charge per mass, but in some instances may not eliminate the target-charging problem. Furthermore, moderate to high current ion beams may suffer from a significant space charge-induced defocusing of the beam that tends to inhibit transporting a well-focused beam over long distances. Again, due to their lower charge per mass relative to conventional ion beams, GCIBs have an advantage, but they do not fully eliminate the space charge transport problem.
A further instance of need or opportunity arises from the fact that although the use of beams of neutral molecules or atoms provides benefit in some surface processing applications and in space charge-free beam transport, it has not generally been easy and economical to produce intense beams of neutral molecules or atoms except for the case of nozzle jets, where the energies are generally on the order of a few milli-electron-volts per atom or molecule, and thus have limited processing capabilities. More energetic neutral particles can be beneficial or necessary in many applications, for example when it is desirable to break surface or shallow subsurface bonds to facilitate cleaning, etching, smoothing, deposition, amorphization, or to produce surface chemistry effects. In such cases, energies of from about an eV up to a few thousands of eV per particle can often be useful. Methods and apparatus for forming such Neutral Beams by first forming an accelerated charged GCIB and then neutralizing or arranging for neutralization of at least a fraction of the beam and separating the charged and uncharged fractions are disclosed herein. Although GCIB processing has been employed successfully for many applications, there are new and existing application needs not fully met by GCIB or other state of the art methods and apparatus, and wherein accelerated Neutral Beams may provide superior results. For example, in many situations, while a GCIB can produce dramatic atomic-scale smoothing of an initially somewhat rough surface, the ultimate smoothing that can be achieved is often less than the required smoothness, and in other situations GCIB processing can result in roughening moderately smooth surfaces rather than smoothing them further.
Historically, when conventional ion beams and GCIBs have been used for workpiece processing, repeatability of processing results has been achieved by using a process dosimetry technique that employs measurement of beam electrical current at the workpiece, integrated over time, and taking into account the size of the processed area to determine a dose in ions/cm2. By controlling the dose (ions/cm2) and the beam energy, good repeatability is achieved for most processes. Often other factors must also be controlled to achieve the desired process results (such as limiting workpiece temperature excursions and beam direction of incidence during processing, etc.) but the dose in ions/cm2 and the beam energy are often the main processing parameters that are controlled to produce repeatable results.
In the case of Neutral Beams and Dissociated Neutral Beams, because the beam particles are not charged, their flux cannot be determined by a current measurement, and thus some other method of dosimetry is required, when acceptable processing results depend on precision control of the processing dose.
It is therefore an object of this invention to provide diagnostic methods and apparatus for characterizing Neutral Beams and Dissociated Neutral Beams.
It is a further object of this invention to provide diagnostic methods and apparatus for characterizing Neutral Beams and Dissociated Neutral Beams to a degree that enables more precise process dosimetry that results in repeatable workpiece processing.